The power transmitting apparatus of a vehicle, such as an automobile, is required not only to perform the transmission of engine power of the automobile to the wheels but also to permit radial, axial and moment displacement from the wheels caused during bounds on rough road running or turning of the vehicle. Accordingly, one end of a drive shaft, interposed between an engine side and a driving wheel side, is connected to a differential gear, via a constant velocity universal joint of the sliding type. The other end is connected to driving wheels via a wheel bearing apparatus including a fixed type constant velocity universal joint.
Recently, it is desirable to improve fuel consumption in view of resource savings or anti-pollution. For meeting such a demand, it has been strongly noticed and desired to reduce the weight of automobile parts, especially wheel bearing apparatus. Although various wheel bearing apparatus has been proposed to reduce weight, it is also desirous to reduce the cost of assembly and disassembly of the wheel bearing apparatus at automobile assembling sites or automobile maintenance markets.
A wheel bearing apparatus 50 shown in FIG. 5 is a representative example. A double row rolling bearing 51 and a constant velocity universal joint 52 are detachably connected to each other. The double row rolling bearing 51 includes an outer member 53, an inner member 56, and double row balls 58, 58. The flange 53b has an integrally formed body mounting flange 53b. The flange 53b is mounted on a body of a vehicle. Double row outer raceway surfaces 53a, 53a are formed on the inner circumference of the outer member 53. The inner member 56 includes a wheel hub 54 and an inner ring 55. The wheel hub 54 has, on its one end an integrally formed wheel mounting flange 54 to mount a wheel (not shown). An inner raceway surfaces 54a is arranged opposite to one of the double row outer raceway surfaces 53a, 53a. A cylindrical portion 54c axially extends from the inner raceway surface 54a. The inner ring 55 is press-fit onto the cylindrical portion 54c of the wheel hub 54. The inner ring 55 has an inner raceway surface 55a arranged opposite to the other of the double row outer raceway surfaces 53a, 53a. The double row balls 58, 58 are disposed between the outer and inner raceway surfaces and rollably held by cages 57. The inner ring 55 is axially immovably secured by a caulked portion 59. The caulked portion 59 is formed by plastically deforming the end of the cylindrical portion 54c radially outward. Furthermore, an end face of the caulked portion 59 is formed with a face spline 59a that is formed simultaneously with the formation of the caulked portion 59.
Seals 60, 61 are mounted on annular openings formed between the outer member 53 and the inner member 56. The seals 60, 61 prevent leakage of grease sealed in the bearing and the entry of rain water or dust into the bearing.
The constant velocity universal joint 52 includes an outer joint member 62, joint inner ring 63, a cage 64, and torque transmitting balls 65. The outer joint member 62 has a cup-shaped mouth portion 66, a shoulder portion 67 forming a bottom of the mouth portion 66, and a hollow shaft portion 68. The shaft portion 68 axially extends from the shoulder portion 67. A female thread 68a is formed on an inner circumference of the shaft portion 68. An end face of the shoulder portion 67 is formed with a face spline 67a. This face spline 67a engages the face spline 59a formed on the end face of the caulked portion 59. Thus, the rotational torque from a drive shaft (not shown) can be transmitted to the wheel mounting flange 54b via the constant velocity universal joint 52 and the inner member 56.
A fastening bolt 69 is fastened to the female thread 68a of the shaft portion 68 of the constant velocity universal joint 52. Accordingly, both the opposite face splines 67a, 59a of the outer joint member 62 and the inner member 56 are press-contacted to each other. Thus, the double row rolling bearing 51 and the constant velocity universal joint 52 can be detachably united. This contributes to reduction of weight and size as well as simplification of assembly and disassembly of the wheel bearing assembly (see JP 63-184501 A)
However, in such a prior art wheel bearing apparatus 50, as shown in FIG. 6, the face spline 59a of the caulked portion 59, formed simultaneously with the formation of the caulked portion 59, is processed at a higher caulking degree than the usual caulking degree. Accordingly, it is believed that cracks would be caused in the face spline 59a. Especially the crack generation rate would be increased at a radially outermost tooth bottom of the face spline 59a where the caulking is performed at a highest degree.
In addition, the specifications of the face spline 59a are required to satisfy demands of automobile manufacturers. Thus, it is impossible to largely change the specifications. Accordingly, it is difficult to adopt free designs to suppress the generation of cracks.